Should I wait for my work visa before starting my job as a junior web developer in Thailand?

From my own experience, the process itself is not so complex, if your employer is legally registered and have proper documents, and is actually willing to give you work permit. The prerequisite is to have a business visa, that you have to get from outside of Thailand, the company will have to provide you the necessary documents. You cant check for the list available online. Then converting it to the right visa along with work permit is a 1day appearance at the designated center. Mine was done by an agency, handled by HR dept, i just had to take a simple medical test and then appeared in person to that center in Chamchuri square, waited for an hour while the agent did all the running, called infront of an immigration officer sitting there. She asked me about my work an basic socializing questions, and issued the 1 year reentry permit and work-permit then and there. I think it depends on the company, if everything is in order and they are actually willing to give you work permit, rest should not be much trouble. Good luck!

A lot of companies may drag their feet or want you to work a probationary period without it. It's illegal but like China it's often ignored

It is so easy. You are not allowed in Thailand to work without a Work Permit and the right Visa. If your company wants you to work before the paper works is done just remember: The fine for you as employee is between 20.000 and 100.000 Thb and/or 5 years prison and for the company between 400.000 and 800.000 Thb. If they are wllling to take the financial risk and compensate you for 5 years prison, please get that on official dubbel checked contracts you are fine if you wish to do the time.

If you happen to get arrested working without a visa it's you who will be in trouble. Act accordingly.

Out of all the teachers I know in Thailand, everyone had a SETV and started working right away. I know this is not right but thats what happened. You need 14 days on your visa toe be able to finalise the last step. It takes quite a while and schools don't want to wait. This is government schools and private schools. Don't know about Int schools. And I have no knowledge about any other line of work.